2.8 KiB
Debugging Notes
Checkpoint
This code:
F000:F9E9 B000 MOV AL,00
F000:F9EB E620 OUT 20,AL
triggers the following warning:
notice: PIC0(0x20): unsupported OCW2 automatic EOI command: 0x00
and the very next instruction:
F000:F9ED E6A0 OUT A0,AL
triggers the same warning:
notice: PIC1(0xA0): unsupported OCW2 automatic EOI command: 0x00
Checkpoint
There's a loop at F000:B5AA that stores 0x4000 DWORDs into RAM (ie, 64Kb), where each DWORD is a single-bit left rotation of the preceding DWORD. This is followed by another loop that loads each DWORD and verifies that it contains the appropriate bit.
Then a stack is set up in RAM (at 0030:0100) and the first CALL is issued:
F000:BC2E E87DEC CALL A8AE
There's some CMOS I/O activity, serial and parallel port I/O, more CMOS I/O, and then some EGA I/O.
When arrive here:
C000:016D B80700 MOV AX,0007
C000:0170 CD10 INT 10
and we complain that the IDTR limit for the real-mode IDT isn't 0x3FF (it's been set to 0xFFFF instead). That may be OK, but I need to verify that that's what the ROM intended. If it is, then I'll probably need to change our assertion from "cpu.addrIDTLimit == 0x03FF" to "cpu.addrIDTLimit >= 0x03FF".
Checkpoint
The BIOS now progresses as far as F000:F747 (PUSH GS).
Checkpoint
The BIOS now progresses as far as 0030:8618 (MOV AX,GS).
Checkpoint
The BIOS now progresses to a Compaq memory-mapped write operation:
stopped (27129586 ops, 2209813 cycles, 361 ms, 6121366 hz)
EAX=000098FC EBX=0000E000 ECX=00000000 EDX=00000000
ESP=000000E4 EBP=00000000 ESI=0000FFFF EDI=00007FBE
SS=0028[00000300,FFFF] DS=0050[80C00000,FFFF] ES=0048[00FF0000,FFFF]
CS=0030[000F0000,FFFF] FS=0000[00000000,FFFF] GS=0304[00003040,FFFF]
LD=0000[00000000,0000] GD=[0001C000,005F] ID=[000FF821,0007] TR=0000 A20=ON
CR0=0000FFF1 CR2=00000000 CR3=00000000 PS=00000083 V0 D0 I0 T0 S1 Z0 A0 P0 C1
0030:8637 C6060000FC MOV [0000],FC ;history=1
and then gets stuck loading CS:IP of 0x28:0xF4AC:
assertion failure in deskpro386.cpu386
Fault 0x0D blocked by Debugger
stopped (27572151 ops, 443210 cycles, 340635 ms, 1301 hz)
EAX=0000FFF1 EBX=00000080 ECX=0000270F EDX=0000004A
ESP=000000FE EBP=00000000 ESI=00007FB6 EDI=00008000
SS=0030[00000300,FFFF] DS=0040[00000400,FFFF] ES=0000[00000000,FFFF]
CS=F000[000F0000,FFFF] FS=0000[00000000,FFFF] GS=0304[00003040,FFFF]
LD=0000[00000000,0000] GD=[00FF0730,0047] ID=[00000000,FFFF] TR=0000 A20=OFF
CR0=0000FFF1 CR2=00000000 CR3=00000000 PS=00000082 V0 D0 I0 T0 S1 Z0 A0 P0 C0
F000:F4A7 EAACF42800 JMP 0028:F4AC
This code will fail if the A20 line is off. Until I can figure out why this code is being run with A20 off, I've worked around it by enabling A20 internally whenever protected-mode is active.